1. Field of the Invention
The invention relates to a zoom tracking apparatus of, for example, an inner focusing lens for controlling the position of the focusing lens to an in-focus position so as to follow the motion of the zoom lens in a manner such that a focal point is not deviated when the zoom lens is moved.
2. Description of the Prior Art
To reduce the size and weight of a video camera, an inner focusing lens is used in an optical system of the video camera. In the case of the inner focusing lens, a zoom lens and a focusing lens are arranged in a lens assembly and the zoom lens and the focusing lens can be moved by an actuator such as a stepping motor, linear motor, or the like.
In the optical system of the video camera, the tracking position of the focusing lens is controlled so as to follow the motion of the zoom lens in a manner such that a focal point is not deviated when the zoom lens is moved. In the case of the inner focusing lens, since the zoom lens and the focusing lens cannot be directly moved, it is difficult to execute such a tracking control by using a mechanical cam. Therefore, in the case of the inner focusing lens, by setting a driving amount of the focusing lens in accordance with the motion of the zoom lens, the tracking control is performed. Such a control is also called an electronic cam.
The position of an object always changes. Therefore, in the case of executing the automatic focusing control of the video camera, it is necessary to always control the position of the focusing lens in accordance with the motion of the object.
In an automatic focusing circuit of a video camera of the image processing system, by using a principle such that an integrated level of middle and high frequency components in an image pickup signal is maximum at the in-focus position, the middle and high frequency component level in the image pickup signal is detected. The middle and high frequency component level in the image pickup signal is integrated in a predetermined focusing area and an evaluation value is obtained. The position of the focusing lens is controlled so that the evaluation value becomes maximum.
In the case of the automatic focusing circuit of the video camera of the image processing system, in order to control the in-focus position in correspondence to the motion of an object to be photographed, the focusing lens or the image pickup device is wobbled back and forth. A peak value of the evaluation values is detected, thereby controlling the position of the focusing lens in accordance with the motion of the object to be photographed.
As mentioned above, in the case of the inner focusing lens, when the zoom lens is moved, it is necessary to control tracking of the focusing lens in accordance with characteristics showing the relation between the position of the zoom lens and the in-focus position of the focusing lens. In the case of the automatic focusing circuit of the video camera of the image processing system, it is necessary to wobble the focusing lens or the image pickup device in the front and back directions and to control the in-focus position in correspondence to the motion of the object to be photographed.
Therefore, in the case of executing the automatic focusing control of the video camera of the image processing system by using the inner focusing lens, when the zoom lens is moved, the tracking control and the wobbling control must be simultaneously performed. However, in order to simultaneously execute the tracking control and the wobbling control as mentioned above, complicated processes are necessary.